You can renumber multiple documents within the same label by removing the label, sorting in the desired way, and then reapplying the label.  When you apply a designation label or issue in batch edit, it only applies the label to documents that don't already have that label applied. 

If you want the final documents in chronological order, you can gather them all up in a tentative label and then sort that label by chronology and then apply to the final label.